Sterility control of food product by introducing a harmless non-sterile component

ABSTRACT

A liquid food product, such as a soup or sauce, is treated by first sterilizing it, e.g. by UHT processing, and then introducing into it a minor amount, e.g. 5 to 15 vol. %, of a non-sterile component, e.g. a dairy product, substantially free of all micro-organisms liable to cause disease. The non-sterile component will cause evident harmless spoilage of the product after a given period of storage, so that the consumer will be obliged to discard the product before any harmful bacteria have grown.

This invention relates to liquid food products such as soups and sauces,and to methods of treating such products so as to extend theirpermissible shelf life.

Soups, sauces, and other liquid food products of low acidity (pH>4.5)can provide an ideal environment for the growth of micro-organisms. Theyare generally made from a wide variety of ingredients and can carry awide range of initial micro-organisms. Treatment at high temperatureunder pressure (UHT processing) substantially sterilizes the product,but micro-organisms remaining in minute amounts or entering thepackaging can produce the risk of food poisoning or other diseases.Consequently, if the packaging is not aseptic the permitted shelf lifemust be short (of the order of days). Aseptic packaging increases thecost of the product to the consumer.

The present invention is based on the idea of introducing into asterilized liquid food product a known micro-biological contaminantwhich will cause evident spoilage of the product after a given period ofstorage, so that the consumer will be obliged to discard the productbefore any harmful bacteria have grown.

The invention provides a liquid food product comprising a majorcomponent which is substantially sterile and a minor component which isnon-sterile but substantially free of all micro-organisms liable tocause disease.

The invention also provides a method of treating a liquid food product,comprising sterilizing the food product and then introducing into it aminor amount of a non-sterile component substantially free of allmicro-organisms liable to cause disease.

The preferred sterilization procedure is heating above 100° C. atsuperatmospheric pressure, but any other convenient procedure may beused, e.g. irradiation.

The non-sterile component may be any suitable medium carrying one ormore types of food spoilage micro-organism, in such a quantity thatafter mixing with the sterile component there are sufficient foodspoilage organisms to substantially ensure that, after packing,preferably in a hermetically sealed container, there will be at leastone spoilage organism per pack. The number of spoilage organismsrequired in each batch of the food product will depend on the pack size:the larger the pack size, the lower the number of organisms required. Itis preferable for the non-sterile component to be a natural foodsubstance, of animal or vegetable origin, produced under conditions inwhich it is free of disease-causing micro-organisms but will inevitablycontain food-spoiling bacteria. Such substances, e.g. raw or pasteuriseddairy products, are cheap and readily available, and they may enhancethe flavour of the product.

Since the food spoilage eventually caused by the non-sterile componentwill be evident to the consumer, it will prevent him from consuming thefood product after the nominal permitted storage period has elapsed. Inthe absence of such evident spoilage, a food product might be kept fortoo long and become contaminated with harmful, not readily detectablebacteria. Suitable evidence of spoilage may be a change in texture(thickening), appearance (colour), and/or smell.

EXAMPLE Production of Fresh Soups and Sauces

After prior preparation, the ingredients of the soup or sauce are mixedin an agitated processing vessel and are subjected to a short period ofprocessing at high temperature under pressure. The time and thetemperature depend on the ingredient mixture and the size of anyparticulates in the liquid phase.

The product is then rapidly cooled by vacuum to 100° C., when apredetermined quantity of raw or pasteurised dairy products are added tothe batch by vacuum (5 to 15% by volume).

The temperature of the batch is then stabilised at 75°-85° C.and theproduct is fed via sterile pipework and filled into clean containersensuring that the temperature after filling is in excess of 75° C.(pasteurisation temperature).

The containers are immediately sealed and held for two minutes to ensurepasteurisation of the container. They are then rapidly cooled torefrigerated storage temperatures and are ready for distribution underrefrigerated conditions.

No artificial food additives or stabilisers are used in the finalproduct or as processing aids.

The process is applicable to a wide range of low acid liquid foodswhere:

the initial ingredients may carry varied and non-specificmicrobiological load;

dairy products which have not been subjected to UHT processing (e.g. rawmilk and cream, pasteurised milk, skimmed milk, or cream) are usable asone of the ingredients;

the packaging system is clean but not aseptic. The containers used maybe gabletopped cartons manufactured under the trade mark "Purpak".

The use of high temperature short time cooking effectively kills theinitial loading of bacteria and renders the product commercially sterileand the product can be considered free of micro organisms.

The addition of the dairy products (described above) at the stagedescribedabove acts as a microbiological flag. While the heat treatmentof the dairyproducts will kill all vegetative organisms, certain heatresistant spores which are invariably present in pasteurised milk willsurvive (mainly of the Bacillus group).

These spores have known and predictable growth patterns and will serveto spoil the product after given periods at differing temperatures. Theywillcause obvious signs of food spoilage and serve to warn consumersthat the product is potentially unsafe. During the process a sufficientquantity ofdairy product is added to ensure that there is not less thanone spoilage organism per pack.

The process ensures that after packing the product has a very lowinitial microbe count and that therefore under optimal storageconditions will have an extended life, but at the same time it ensuresthat certain naturally occurring food spoilage organisms are present.

The spores in dairy products after pasteurisation are of a particulartype,with known behavioural and growth patterns. They have certainbeneficial characteristics which will reduce the risks of foodpoisoning:

under refrigerated conditions they will grow slowly but will not spoilthe product until it has past its commercial shelf life;

they will provide competition for (and therefore reduce the growth rateof)any food poisoning organisms which may contaminate the product as aresult of poor process control or post process contamination occurringwhile the product is in the control of the manufacturer, distributor, orfinal consumer;

they will grow faster than known food poisoning organisms, thus obviousfood spoilage will occur before any food poisoning bacteria has grownsufficiently to produce dangerous levels of toxins; they will growquicklyif the product is not refrigerated or is otherwise abused, andwill cause obvious food spoilage.

I claim:
 1. In a method for treating and packaging a liquid food productfor temporary storage under controlled conditions and distribution toconsumers, comprising the steps of sterilizing the food product and thensealing it in a container, the improvement comprising introducing intothe food product, after the sterilization step and before the sealingstep, a non-sterile component substantially free of all micro-organismsliable to cause disease but containing food-spoilage bacteria forcausing evident spoilage of the food product after a given period ofstorage under controlled conditions.
 2. A method as claimed in claim 1,in which the non-sterile component is a natural food substance producedunder conditions in which it is free of disease-causing micro-organismsbut will inevitably contain food-spoilage bacteria.
 3. A method asclaimed in claim 2, in which the non-sterile component comprises a dairyproduct.
 4. A method as claimed in claim 2, in which the non-sterilecomponent is pasteurised.
 5. A method as claimed in claim 1, in whichthe sterilization of the food product comprises heating above 100° C. atsuperatmospheric pressure.
 6. A method as claimed in claim 1, in whichthe non-sterile component makes up 5 to 15% by volume of the resultingproduct after treatment.
 7. A method as claimed in claim 1, in which thefood product is a soup or sauce.
 8. A method as claimed in claim 1, inwhich the food product is of low acidity, i.e. pH >4.5.
 9. A method asclaimed in claim 1, in which the introduction of the non-sterilecomponent and the sealing of the container take place at pasteurizationtemperature.
 10. An article of commerce made by the method of claim 1.